1. Field of the Invention
The present invention relates to novel antibodies and methods of using the antibodies to inhibit blood coagulation. In particular, the invention relates to novel antibodies that can specifically bind native human tissue factor with high affinity. The antibodies of the invention are useful for a variety of applications, particularly for reducing blood coagulation in vivo.
2. Background
Blood clotting assists homeostasis by minimizing blood loss. Generally, blood clotting requires vessel damage, platelet aggregation, coagulation factors and inhibition of fibrinolysis. The coagulation factors act through a cascade that relates the vessel damage to formation of a blood clot (see generally L. Stryer, Biochemistry, 3rd Ed, W.H. Freeman Co., New York; and A. G. Gilman et al., The Pharmacological Basis of Therapeutics, 8th Edition, McGraw Hill Inc., New York, pp. 1311-1331).
There is general agreement that factor X (FX) activation to factor Xa (FXa) is a critical step in the blood coagulation process. Generally, FX is converted to FXa by binding a catalytically active complex that includes "tissue factor" (TF). TF is a controllably-expressed cell membrane protein that binds factor VII/VIIa to produce the catalytically active complex (TF:VIIa). A blood clot follows FXa-mediated activation of prothrombin. Blood clotting can be minimized by inactivation of TF to non-native forms which cannot optimally produce the TF:VIIa complex. Excessive formation of FXa is believed to contribute to various thromboses including restenosis.
Thrombosis may be associated with invasive medical procedures such as cardiac surgery (e.g. angioplasty), abdominothoracic surgery, arterial surgery, deployment of an implementation (e.g., a stent or catheter), or endarterectomy. Further, thrombosis may accompany various thromboembolic disorders and coagulopathies such as a pulmonary embolism (e.g., atrial fibrillation with embolization) and disseminated intravascular coagulation, respectively. Manipulation of body fluids can also result in an undesirable thrombus, particularly in blood transfusions or fluid sampling, as well as procedures involving extracorporeal circulation (e.g., cardiopulmonary bypass surgery) and dialysis.
Anti-coagulants are frequently used to alleviate or avoid blood clots associated with thrombosis. Blood clotting often can be minimized or eliminated by administering a suitable anti-coagulant or mixture thereof, including one or more of a coumarin derivative (e.g., warfin and dicumarol) or a charged polymer (e.g., heparin, hirudin or hirulog). See e.g., Gilman et al., supra, R. J. Beigering et al., Ann. Hemathol., 72:177 (1996); J. D. Willerson, Circulation, 94:866 (1996).
However, use of anti-coagulants is often associated with side effects such as hemorrhaging, re-occlusion, "white-clot" syndrome, irritation, birth defects, thrombocytopenia and hepatic dysfunction. Long-term administration of anti-coagulants can particularly increase risk of life-threatening illness (see e.g., Gilman et al., supra).
Certain antibodies with anti-platelet activity have also been used to alleviate various thromboses. For example, ReoPro.TM. is a therapeutic antibody that is routinely administered to alleviate various thromboembolic disorders such as those arising from angioplasty, myocardial infarction, unstable angina and coronary artery stenoses. Additionally, ReoPro.TM. can be used as a prophylactic to reduce the risk of myocardial infarction and angina (J. T. Willerson, Circulation, 94:866 (1996); M. L. Simmons et al., Circulation, 89:596 (1994)).
Certain anti-coagulant antibodies are also known. Particularly, certain TF-binding antibodies have been reported to inhibit blood coagulation, presumably by interfering with assembly of a catalytically active TF:VIIa complex (see e.g., Jeske et al., SEM in THROM. and HEMO, 22:213 (1996); Ragni et al., Circulation, 93:1913 (1996); European Patent No. 0 420 937 B1; W. Ruf et al., Throm. Haemosp., 66:529 (1991); M. M. Fiorie et al., Blood, 8:3127 (1992)).
However, current TF-binding antibodies exhibit significant disadvantages which can minimize their suitably as anti-coagulants. For example, current TF-binding antibodies do not exhibit sufficient binding affinity for optimal anti-coagulant activity. Accordingly, for many thrombotic conditions, to compensate for such ineffective binding affinities, unacceptably high antibody levels must be administered to minimize blood coagulation. Further, current TF-binding antibodies do not effectively discriminate between native TF and non-native forms of TF, i.e. the current antibodies do not exhibit sufficient binding specificity. Still further, current TF-binding antibodies can not prevent FX from binding to TF and/or TF:VIIa complex.
It would thus be desirable to have an anti-coagulant antibody that binds native human TF with high affinity and selectivity to thereby inhibit undesired blood coagulation and the formation of blood clots. It would be further desirable to have such an anti-coagulant antibody that prevents the binding of Factor X to TF/VIIa complex.